摘要:

Abstract.1Despite apparent directional sexual selection in favour of large body size, males of the anthophorine beeCentris pallidaremain highly variable in body size.2One possible cause of persistent size variation among males is geographic variation in the extent of the large male mating advantage. However, a study of a population in an area not previously investigated revealed that the large male mating advantage was as strong here as it has been elsewhere in other years.3Although the reproductive benefits of being large were consistent in populations separated spatially and temporally, the intensity of bird predation on mate‐searching males varied greatly between locations.4The bee‐killing birds focused exclusively on bees which were digging down to meet emerging females or fighting on the ground, never on flying males. Males which were collected on the ground by hand (to simulate avian predation) were significantly larger on average than flying males collected by sweep netting.5Therefore, in some location in some years, sexual selection in favour of large body size may be opposed by natural selection exerted by predators, perhaps contributing to the maintenance of size variation in this

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00422.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1In tropical savanna environments rainfall is often very seasonal, so that much of the year is characterized by a long and unpredictable dry season. Because the timing and availability of rain exerts a major influence on plant growth and production, many species during the dry period exhibit dramatic reduction in leaf quality. Accordingly, and kind of behaviour shown by phytophagous insects that synchronizes larval feeding with food availability will be adaptive.2The reproductive status of threeMycalesisbutterflies was monitored over a 2‐year period (1989–90) in north‐eastern Queensland, Australia, at a lowland site (Cardwell, 18°16's, 146°02′E) which experiences a pronounced dry season. Females of these species and of five other satyrines (Ypthima, Hypocystaspp.) were also examined less intensively during the dry season in areas throughout northern and central Queensland, north of the tropic of Capricorn.3These relatively sedentary butterflies exhibit three different strategies for dealing with the unpredictable dry period and associated deterioration of larval food plants (grass). First, five species appear to breed continuously, though for most reproductive activity (mature egg number) declines markedly in the late dry season. Two of these (Hypocysta irius, H.metirius) are restricted to less seasonal and more favourable (wetter) areas but the three others (Ypthima arctous, H.adiante, H.pseudirius) occur widely in the relatively dry savanna, where they may specialize on grass in moister microenvironments. Second, two species (M.terminus, M.sirius) live in predictably moist habitats which are buffered from climatic extremes; they breed for much of the season but reproductive activity declines as the dry season progresses and may cease late in the season. Third, one species (M.perseus) is more opportunistic, breeding for only a limited interval during the favourable (wet) periods; during the long dry season adults contract to moist refugia and remain in reproductive diapause.4Spending the late dry season as an adult, either in diapause or with mature eggs, may improve the capacity to utilize new growth of grasses at the start of the favourable season, thereby enhancing population growth during good times. It may also provide additional flexibility to counter the temporal uncertainty of the dry season.5The strategy of residing in more equitable habitats or specializing on predictable foods may be the most restrictive in terms of dis

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00423.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1The Tritrophic and Enemy Impact concepts predict that natural enemy impact varies: (a) among plant genotypes and (b) may depend on the abundance of heterospecific herbivores, respectively. I tested these predictions using three herbivore species on potted, cloned genotypes ofSalik sericeaMarshall in a common garden experiment.2Densities of the leaf miner (Phyllonorycter salicifoliella(Chambers)) and two leaf galling sawflies (Phyllocolpa nigrita(Marlatt) andPhyllocolpa eleanoraeSmith and Fritz) varied significantly among willow clones, indicating genetic variation in resistance.3Survival and natural enemy impact caused by egg and larval parasitoids and/or unknown predators differed significantly among willow clones for each of the three herbivore species, indicating genetic variation in survival and enemy impact.4Survival ofPhyllonorycterwas negatively density‐dependent among clones.5Survival ofPhyllonorycterandPhyllocolpa eleanoraewere positively correlated with densities of heterospecific herbivores among clones and parasitism of these species were negatively correlated with densities of the same heterospecific herbivores among clones.6At least forPhyllonorycterthis positive correlation may suggest either facilitation of survival between herbivore species, which do not share natural enemies, or an apparent interaction caused by host plant genetic variation.7Among clones, egg parasitism ofPhyllocolpa eleanoraewas weakly positively correlated with density ofPhyllocolpa nigrita. Since these species share the sameTrichogrammaegg parasitoid, this interaction could support the hypothesis of apparent competitio

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00424.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1The larvae of the multivoltine imported willow leaf beetle,Plagiodera versicolora(Laicharting), are found in larval aggregations during the first half of the larval stage. An experimental study was conducted to test for seasonal (brood) and group size effects on larval fitness. For each of the three broods, egg group sizes of1, 4, 8, 16, 24 and 32 were established in the field and monitored for the first 6 days post‐hatching.2There was no effect of group size on larval weight, but there was a significant effect of group size on survival. Individuals from group size 16 had the highest survival, which coincides with the mean natural cluster size of 15.3 eggs.3There were no significant interactions between brood and group size.4The effect of larval weight on adult fitness was determined in the laboratory and the field. Larval weight was correlated with egg production in the laboratory but not in the fiel

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00425.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1The adaptation of the non‐migratory galling aphidKaltenbachiella japonica(Matsumura) to the budburst phenologies of individual host trees (Ulmus davidianavar.japonicaNakai) was investigated. There was a large variation in budburst time between individual host trees. We tested a hypothesis that aphid populations on respective host trees are genetically differentiated through adaptation to the budburst phenologies of host trees.2There was significant correlation between the budburst time of eight host trees in two successive years.3Tree‐associated populations differed significantly in egg‐hatching time, and the mean hatching time was significantly correlated with the mean budburst time of respective host trees.4Mating was made between male and female sexuales of the same clone (i.e. self‐mating) to obtain selfed eggs. Hatching patterns of selfed eggs showed that there was a substantial amount of genetic variance in hatching time between clones (galls). Nested ANOVA demonstrated that the between‐tree component contributed more to the phenotypic variance than the within‐tree or within‐gall components.5Reciprocal crosses between males and females of different clones furthermore demonstrated significant differences in hatching time between cross combinations, but no significant differences between the two reciprocals within combinations. This result suggests that there are no maternal effects for the timing of egg hatch and that the differences between selfed lines are attributable to genetic variance.6The fine‐scale adaptation hypothesis was supported by egg‐hatching experiments, which further suggest that budburst phenology varying between individual trees is acting as intense selective pressure on the egg‐hatching time of

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00426.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1We censused ectoparasite populations of adult and nestling swifts over the course of the host's breeding season. Nearly all of the birds were infested with chewing lice and two‐thirds of the nests were infested with louse flies. Feather mites were observed but not quantified.2Lice and louse flies both showed aggregated distributions among hosts. Louse eggs, hatched lice and adult louse flies had negative binomial distributions, whereas the aggregated distribution of louse fly pupae was not adequately described by negative binomial or Poisson models.3Transmission of lice from parents to offspring was documented. A comparison of the age structure of lice on parents and offspring indicated that most transmission was by nymphal lice.4Host reproductive success and survival appeared to be independent of the number of lice or louse flies. Neither parasite correlated with the number, body mass, or date of fledging of young birds, nor with the overwinter survival of adults. We caution, however, that experimental manipulations of parasite load are required for a definitive test of the impact of ectoparasites on evolutionary fitness component

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00427.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1Foraging patterns of the squash beetle,Epilachna borealisFabricius (Coleoptera: Coccinellidae), in field cages are not consistent with the hypothesis that this beetle avoids leaves in which its feeding damage has caused the induction of cucurbitacins.2E.borealisfeeding does not induce accumulation of cucurbitacins inside or outside of feeding trenches.3Cucurbitacins do not reduce the survival or growth rate ofE. borealislarvae.4High concentrations of cucurbitacins fail to deterE.borealisfeeding; rather, cucurbitacins are feeding stimulants for squash beetles.5Trenching behaviour inE.borealisis facultative and correlates with leaf turgor and the degree to which sticky phloem sap oozes from damaged leaves.6Mucilaginous phloem sap in many curcurbit species inhibits feeding byE.borealiswhen it is applied to beetle mouthparts.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00428.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1Competitive interactions among larvae ofDrosophilaspecies using the same habitat will usually involve individuals varying in age and size. Older, larger larvae might be expected to outcompete younger, smaller larvae.2Newly hatched laryae ofDrosophila aldrichiandD.buzzatiiwere placed on induced cactus necroses (simulating the natural habitat), either simultaneously, or with a 1 or 2 day difference in the time at which individuals of the other species were added.3Evidence for competitive differences with larval age were found. In both species, body weight was significantly higher for those larvae added first than for later addition larvae, and a longer time to complete development was required for those larvae added 2 days later. However, pre‐adult viability ofD.aldrichiwas significantly higher for larvae started 1 or 2 days after larvae ofD.buzzatii. ForD.buzzatii, viability was lowest for larvae started simultaneously withD.aldrichi, but not different between those started either before or afterD.aldrichi.4Considering all three traits, no clear advantage for the early addition larvae was observe

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00429.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1Competition is shown to be occurring within and between the congenersCoelopa frigidaandC.pilipes;it is noted that the two species frequently coexist despite ongoing competition.2Observations on natural wrack‐beds indicate that there is a marked difference in the distributions of the larvae:C.frigidalarvae aggregate in cooler parts of the bed,C.pilipesin warmer parts. This difference in microdistribution reflects a broader‐scale difference in the geographical distributions of the species ‐C.pilipesbeing the more southerly of the two.3The larval distributions are shown to be caused primarily by the behaviour of the larvae themselves ‐ not by choices made by ovipositing females, nor (at least to any great extent) by differential survival.4The different micro‐distributions within beds constitute a form of niche difference which will cause competitive abilities to be frequency‐dependent and hence have a stabilizing effect. It is possible that this effect may be supplemented by others; and, in particular, effects operating at the level of the‘linear meta‐population’may be worthy of further investigation both inCoelopaand in othe

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00430.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.1The aphidsUroleucon tissotiandU.nigrotuberculatumboth exhibit significantly aggregated distribution patterns across clumps of their common host plantSolidago altissima, the tall goldenrod. However,U.nigrotuberculatumis significantly more aggregated than isU.tissoti. We tested the hypothesis that goldenrodgenotype‐by‐U.tissotigenotype interactions for aphid performance characters could partially account for this difference.2Only one of the characters we measured showed a significant genotype‐bygenotype interaction; therefore it is unlikely that such interactions affect the distribution ofU.tissotiacross goldenrod stems.3In addition, we found that three environmental variables (genetic variation for resistance to herbivory, host plant morphology, and local host density) affect the degree of aggregation found in bothU.tissotiandU.nigrotuberculatumpopula

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1995.tb00431.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY